Incumbent Democrat Mike Thompson, seeking his 15th term, enters the June 2 top-two primary for California's 4th Congressional District with a substantial advantage rooted in his long tenure on the House Ways and Means Committee and established support across Napa, Yolo, and surrounding counties. Challenger Eric Jones, a venture capitalist and nonprofit executive, has mounted the most visible Democratic primary contest by emphasizing affordability, Medicare expansion, and farmworker aid, while multiple Republicans including Ray Riehle and Sharon Brown compete for the second advance spot. The district's composition and Thompson's prior general-election margins above 60 percent underpin trader consensus that he will advance, with the primary outcome also shaping the November matchup under California's nonpartisan system. No major late developments have altered the field ahead of voting.